Whiplash associated disorders (WAD) to the neck are common and debilitating, and often without objective clinical findings. They occur during a motor vehicle impact when the head lags behind the accelerated torso, loading the neck. They can occur in frontal, side and rear impacts but most complaints occur after a rear-end collision by another vehicle. Because of the lack of obvious tissue damage upon clinical examination and diagnostic testing, the pain and ensuing litigation associated with this injury are often considered unjustified or the manifestation of a psychiatric disorder. On the other hand, soft tissue injuries which are undiagnosed clinically may be the source of pain after whiplash. Recent clinical and biomechanical studies implicate the facet joints as perhaps the major source of pain after whiplash. The purpose of this study is to determine ifnociceptors (pain receptors) in the cervical facet oints can be a source of whiplash pain. Histological, neurophysiological and biomechanical techniques have been utilized. Specific Aims: The specific aims of the second phase of this study are: 1. To determine the response of cervical facet nociceptors and mechanoreceptors to low-rate versus high-rate loading. 2. To determine the response ofparaspinal muscles to low-rate and high-rate facet capsule stain. 3. To determine the morphology of the human cervical facet joint capsules, including the ventral aspect of the joint and synovial folds. 4. To determine the distribution of nerves and nerve endings in the human facet joint capsule, with focus on anterior aspects and synovial folds. Immunocytochemistry will be used to identif2? nerves containing substance P (SP) and calcitonin gene related peptide (CGRP), neuropeptides associated with pain and beta amyloid precursor protein betaAPP).